let cssObj = {
    'background-color': '#F7F7F7',
    'color': '#AFAFAF'
};

function chooseAmount(amount) {
    $('.amount-info').each(function (key, item) {
        $(item).css(cssObj);
        $(item).removeClass('gradient')
    });
    let obj = $(amount);
    obj.addClass('gradient');
    obj.css('color', '#FFFFFF');
}